The present invention generally relates to a casing for an electrical or electronic device, and more particularly, to an arrangement for attaching a cover member onto a casing of dielectric coaxial resonators and the like to be employed for a microwave filter, etc.
Generally, a dielectric coaxial resonator, for example, a 1/4 wavelength coaxial TEM resonator 1 as shown in FIG. 1 includes an inner conductor 2, an outer conductor 3 and a dielectric member 4 of a ceramic dielectric material of titanium oxide group, etc. More specifically, the cylindrical or pipe-like dielectric member 4 has a central bore 4h with an inner wall face 4a, and an outer wall face 4b, and a material superior in high frequency conductivity and close adhesion with respect to the dielectric member 4, e.g., silver paste is baked onto the inner wall face 4a and the outer wall face 4b so as to form the inner conductor 2 and the outer conductor 3. In a hollow interior of the inner conductor 2, a central rod 5 of a similar ceramic material and having an axial length longer than that of the dielectric member 4 is fitted and fixed depending on necessity, with one end 6 of the rod 5 which projects outwardly to a certain extent from an open end 7 of the resonator 1 being covered by an electrode film 8 extended from the inner conductor 2. The inner conductor 2 and the outer conductor 3 are short-circuited by another electrode layer 9 at the other end of the resonator 1.
FIG. 2 shows only an essential portion of a conventional dielectric resonator 11 for another example which does not employ the central rod 5 as referred to above. In the resonator 11, the central rod 5 is replaced by a terminal electrode 12 of any proper shape fitted partly into the central bore 4h applied with the inner conductor 2, and fixed by a conductive bonding agent for connection with the inner conductor 2. To the upper portion of the terminal electrode 12 properly shaped and projecting outwardly to a predetermined extent from the open end of the resonator 11, electrodes 23 and 24 each at one side of capacitors 21 and 22 are connected, while the other electrodes 25 and 26 of said capacitors 21 and 22 are connected to corresponding ends of lead wires 27 and 28 whose other ends are further connected, for example, to other resonators, connectors, etc. (not shown). These capacitors 21 and 22 are of chip-type capacitors intended for capacity coupling of the resonator 11 with such external components.
In FIG. 3, there is shown an electrical filter 30 constructed through employment of the resonators as described above, particularly, the resonators 11 as shown in FIG. 2, with like parts in FIG. 2 being designated by like reference numerals.
The filter 30 in FIG. 3 includes a case 40 of a rectangular cubic box-like configuration made, for example, of duralumin or the like, and formed with recesses 51, 52, 53 and 54 of a semi-circular cross section arranged in a parallel relation at predetermined small intervals therebetween. The filter 30 is also formed with grooves 61, 62 and 63 each of a semi-circular cross section, extending between the recesses 51 and 52, 52 and 53, and 53 and 54, and further, formed with grooves 71 and 72 extending between the recess 51 and the outer side of the case 40, and between the recess 54 and the outer side of the case 40 respectively, with the grooves 71, 61, 62, 63 and 72 being aligned on a straight line. After mounting various parts on the case 40 as described hereinbelow, a cover member (not shown) having construction generally similar to that of the case 40 is applied onto said case 40 so as to be fixed by screws for completion of the product.
Into the recesses 51, 52, 53 and 54, the resonators 11A, 11B, 11C and 11D are fitted each by half, with the outer conductors 3 thereof being fixed to the case 40 for electrical conduction. Such fixing is effected, for example, through employment of a conductive bonding agent or by screws. An input coaxial connector 81 is partly fitted in the groove 71, while an output coaxial connector 82 is also partly fitted in the groove 72, and both of these connectors 81 and 82 are fixed to the case 40 and its cover member (not shown) by a conventional practice. A central terminal of the input coaxial connector 81 is connected to the capacitor 21 of the first stage resonator 11A through a lead wire 91. The capacitor 22 of the first stage resonator 11A is connected to the capacitor 21 of the second stage resonator 11B by a lead wire 92 through the groove 61. The capacitor 22 of the second stage resonator 11B is connected to the capacitor 21 of the third stage resonator 11C by a lead wire 93 through the groove 62. The capacitor 22 of the third stage resonator 11C is connected to the capacitor 21 of the fourth stage resonator 11D by a lead wire 94 through the groove 63. The capacitor 22 of the fourth stage resonator 11D is connected to a central terminal of the output coaxial connector 82 by a lead wire 95.
As is seen from the filter construction described so far as one example, the resonators 11 are bonded at the outer conductors 3 thereof to the case 40 and the cover member through employment of a conductive bonding agent, or metallic nets (not particularly shown) of copper and the like are disposed between the outer conductors 3 and the case 40 and cover member, with the metallic nets being soaked with a bonding agent for subsequent fixing of the cover member to the case 40 by screws, which requires an extremely troublesome procedure. Meanwhile, in other known structures, the fixing of the cover member by screws are replaced by bonding of the cover member to the case by a bonding agent or solder, but even in such arrangement, similar problems to those in the screw fixing are also experienced.